Effect of Calcination Conditions on Synthesis of Ultrafine ZrB₂ Powder by Sol-Gel Method

ZrB₂-based ceramics have broad application prospects in the field of ultra-high temperature. ZrB₂ powders are prepared by sol-gel method with zirconium propanol, sucrose and boric acid as Zr, C and B sources, respectively, and the effects of calcination temperature, holding time and argon flow rate on the synthesis of ZrB₂ powder are studied. The results show that with the increase of calcination temperature, the content of impurity phase in the product decreases gradually, and that the content of ZrB₂ phase increases gradually. Pure ZrB₂ powders are obtained by holding the precursor powders with a molar ratio of 2.85∶1∶7 of B∶Zr∶C in argon atmosphere at 1 550 ℃ for 30, 60 and 120 minutes. The average grain size of ZrB₂ powders calculated by Scherrer formula is much smaller than that observed by SEM, indicating that the ZrB₂ powders are composed of small grains. The argon flow rate during calcination process will affect the volatilization degree of B₂O₃, and then affect the phase composition of the product.